Project Summary More than 37 million people are currently living with HIV, an infection that still kills over 1 million individuals per year. Although antiretroviral therapy (ART) has vastly improved over time, it is not curative. The barrier to HIV cure is a reservoir of latent proviruses harbored in resting CD4+ T cells. If a patient ceases ART, HIV will rebound from this reservoir within a matter of weeks, allowing disease progression. HIV cure depends on reversing the latent state of the cells containing provirus, thus allowing the immune system to detect and eliminate them. Unfortunately, the field has yet to find a drug that will do this without life-threatening toxicity. Thus, new cure strategies must be tested in animal models: simian immunodeficiency virus (SIV) and simian- human immunodeficiency virus (SHIV) infected rhesus macaques. The landscape of latent HIV proviruses was recently found to be mostly defective: only 2% of latent proviruses are intact. Because of this, PCR assays that amplify a small part of the proviral genome give an inaccurate, multiple-log overestimate of the latent reservoir. Currently, little is known about the latent reservoir in SIV and SHIV models. It is essential to characterize the pool of latent proviruses in these animals in order to determine whether they are accurate model systems in which to test HIV cure strategies. Once the landscape of proviruses is known, we must design novel assays to accurately measure the latent reservoir in SIV and SHIV models. The only way we can determine whether our cure strategies are working and move therapies to clinical trials is by being able to quantify their effect in our animal models. This proposal will characterize the landscape of latent SIV and SHIV proviruses, design a novel assay to accurately measure only the replication-competent, intact proviruses (the true latent reservoir), and test the effect of candidate latency reversing agents on the latent reservoir using our new assay.